Pyrocarbonic acid dialkyl esters corresponding to the general formula ##STR1## in which R and R' may be the same or different and represent C.sub.1 -C.sub.4, preferably C.sub.1 -C.sub.2, alkyl radicals, more particularly pyrocarbonic acid dimethyl or diethyl esters, are used for a variety of applications. By virtue of their bactericidal and fungicidal activity, they are used, for example, for sterilizing beverages and foods (German Offenlegungsschrift No. 2,223,420, Chem. Abstr. 78 3020 c, U.S. Pat. No. 3,936,269, Chem. Abstr. 76, 71075 h). They are used in veterinary medicine for their inflammation-inhibiting effect and for their ability to accelerate the healing of wounds (German Offenlegungsschrift No. 2,307,827). Their ready decomposability under the effect of heat, optionally in the presence of special catalysts, makes them suitable for use as blowing agents in the production of foamed plastics (French Pat. No. 2,220,564, German Auslegeschriften Nos. 1,694,068 and 1,694,069 and Offenlegungsschrift No. 2,053,399) and foamed glass materials (Offenlegungsschriften Nos. 2,153,532 and 2,318,167). Further applications are, for example, their use as activators for peroxide bleaches (Offenlegungsschrift No. 2,227,602), as activators in the peroxide-catalyzed polymerization of vinyl chloride (U.S. Pat. Nos. 3,584,386 and 3,985,720), as accelerators in the production of polyesters (U.S. Pat. No. 3,542,738) and for improving the flow properties of polyurethane systems.
In storage, the above-mentioned pyrocarbonic acid esters have the property of decomposing gradually--and more quickly under the action of heat--into carbon dioxide and the corresponding dialkyl carbonate (cf., for example, V. I. Kovalenko, J. Gen. Chem. USSR 1952, 22, 1587). As a result, the concentration of solutions containing pyrocarbonic acid esters gradually decreases during storage and considerable pressure can be built up where sealed vessels are used. It is therefore of considerable interest both in terms of economy and in terms of safety to reduce or even completely suppress this decomposition of pyrocarbonic acid esters caused, in particular, by the action of heat.
It is already known that boron compounds, such as, for example, boric acid, pyroboric acid or boron trioxide, can be used for preventing the thermal decomposition of pyrocarbonic acid esters (Chem. Abstr. 76, 13846z). According to another proposal (Chem. Abstr. 78, 147374u), certain metal sulfates are added with a view to achieving the same objective. According to the teaching of these literature references, the crude product is distilled in the presence of the particular stabilizer in order thus to obtain a highly pure product in high yields. However, the particular boron and metal sulfate compounds mentioned in the cited references are insoluble in most organic solvents and, because of this, are unsuitable for the production of stabilized homogeneous solutions of the pyrocarbonic acid esters in inert organic liquids.
Accordingly, the object of the present invention is to provide effective stabilizers for pyrocarbonic acid esters or for solutions containing pyrocarbonic acid esters which are soluble in organic solvents. According to the invention, this object is achieved by the use of the carbonyl, sulfonyl or thiourea compounds described herein.